1. Field of the Invention
The present invention relates to an organic fluorine compound suitable as a dispersing agent for dispersing fine particles of various metals, metal oxides, metal salts, fluorocarbons, fluorine-containing resins, and the like into various resins or the solutions thereof. More particularly, it relates to an organic fluorine compound which is capable of imparting such properties as water repellency, oil repellency, soil resistance, mold release, and rust prevention to the surface of articles obtained from such dispersions and is particularly excellent in dispersion stability.
2. Description of the Prior Art
A ferromagnetic metal film type magnetic recording medium obtained by forming a magnetic layer of cobalt, nickel, iron or an alloy comprising said metals as the principal component by a vacuum film-forming process, such as vacuum vapor deposition, sputtering and ion plating, on a substrate, e.g. a film of polymer such as polyester and polyimide, aluminum alloy sheet, glass sheet, etc. can potentially have a drastically increased recording density. To realize such increased density, however, it is necessary to make the magnetic layer very thin and at the same time to make the surface of the medium as flat as possible. However, since these measures act toward lowering the endurance reliability of said medium, a variety of measures have been investigated with the aim of improving the endurance reliability. For example, in a magnetic disc unit used in the external memory of electronic computers, a so-called contact-start-stop (CSS) system is in use wherein generally the magnetic head floats above the magnetic disc surface when the disc is in operation and contacts with the disc surface when the disc stops. For such a system, a method has been proposed wherein fine irregulalities (protruded parts) are formed on the disc surface, a ferromagnetic metal thin film is then formed thereon, and a protective layer and a lubricant layer are further provided on the ferromagnetic metal thin film, the protective layer comprising graphite, SiO.sub.2 etc. as the main component and the lubricant layer comprising a perfluoropolyether having modified or unmodified molecular terminals.
In magnetic coating materials used in magnetic tapes, magnetic discs, magnetic cards, etc., the dispersibility and the dispersion stability of ferromagnetic fine particles are important factors in manifestation of magnetic properties. Further, when ferromagnetic metal fine particles comprising iron, its alloy, or the like is used as such ferromagnetic fine particles, the storage stability after magnetic coating formation, viewed from the point of rust prevention, is also a important factor. Previously, therefore, hydrocarbons having polar groups, e.g. higher fatty acids or their sulfuric esters, lecithin, and aliphatic phosphoric acid esters, have been used as as surface active agent with the aim of enhancing dispersibility or storage stability.
In order to increase the recording density of a ferromagnetic metal thin film type magnetic recording medium, it is necessary to reduce the floating distance of the magnetic head. In such a case, if the surface configuration of the magnetic disc is improved by reducing the height of protruded parts on the disc surface, it causes lowering of CSS durability and at the same time causes a so-called adsorption phenomenon wherein the lubricant on the disc surface gathers between the magnetic head and the disc during stoppage of the disc unit and resultantly the magnetic head sticks to the disc surface. To solve such problems, therefore, it is important that the lubricant on the disc surface forms a coating layer composed of the lubricant on the protective layer surface and can be easily sheared between the lubricant molecules at the contact point of these coating layers, namely at the sliding surface between the disc and the magnetic head. Since a perfluoropolyether used as a lubricant is covered over almost the whole surface of its molecule with fluorine atoms, it shows a good shearing property between molecules but a weak adhesive force to the disc surface or the magnetic head surface. Although introduction of various polar groups into perfluoropolyether has been proposed to strengthen the adhesive force to the magnetic head surface, the effect of the introduction of polar groups is not satisfactory because perfluoropolyether has itself a high molecular weight of at least 3000, usually 4000 or more, and the effect of improving disc durability is also not marked. On the other hand, when the molecular weight of perfluoropolyether itself is decreased in order to enhance the efficacy of polar groups, it leads to spin-out due to high speed rotation of the disc and vaporization of the polyether itself because interaction between the molecules is weak. Accordingly, reduction of the molecular weight is difficult to adopt in practice.
On the other hand, aliphatic hydrocarbons having polar groups typically represented by stearic acid are excellent in adhesive strength to various surfaces and in disposition toward molecular orientation. However, since they show a stronger interaction between molecules as compared with fluorohydrocarbons, they can hardly give a desired durability when used as the lubricant.
Further, surface active agents for magnetic coating materials previously used have a limitation in their dispersibility and, since the surface roughness of the magnetic layer is determined by the dispersibility, they not only are becoming incapable of meeting the recent demand for higher recording density but have difficulties in that these surface active agents bleed out gradually to the magnetic layer surface to deteriorate the practical performance or cause rusting during storage at high temperature to deteriorate the performance.